The sensor is S1 in this alarm that we found in a Radio Electronics magazine from May 1971. Several sensors can be used in series. The SCR supports equivalents from the 106 series.
This circuit is from an English publication from 1944. The power supply need not be symmetrical. The...
This is an amplifier for alternating signals (AC) with automatic gain control, using an LM3900...
This circuit with reed sensors is very simple, feeding a 12 V siren when triggered. The circuit has a...